1. Field of the Invention
The present invention relates to a rotating spraying type coating apparatus which enables various shapes of spray pattern to be obtained.
2. Description of the Related Art
A typical conventional rotating spray type coating apparatus has heretofore been arranged as follows. A spraying head in the shape of a cylinder, a bell or the like is attached to a rotating shaft or a drive device. A paint supply passage is connected to the proximal end of the spraying head, while a paint radiating portion is formed at the distal end of the spraying head, and air outlet ports for jetting out a stream of a air which bends forwardly the particles of paint radiated from the paint radiating portion are provided in the form of a circular ring. In this arrangement, adjustment of spray patterns is effected by varying the rate of flow of the air jetted out from the air outlet port.
The above-described conventional coating apparatus suffers, however, from the following problems. Even if the flow rate of the jetted air is changed greatly (air flow rate: 0 to 500 l/min), the shape of spray pattern remains in the doughnut-shaped configuration, and there is no substantial change in the width of the spray pattern, which means that the range within which the spray pattern can be adjusted is disadvantageously narrow. It is, needless to say, impossible to obtain an elliptical or dumbbell-shaped spray pattern.
There has been another sort of conventional rotating spraying type coating apparatus in which a multiplicity of air outlet ports are provided around the outer periphery of the spraying head so as to control the air jetted out from the outlet ports in the circumferential direction of the spraying head and to thereby control the shape of the spray pattern (see Japanese Utility Model Laid-Open No. 54-25270). In this prior art, the velocity and width of the stream of air which passes the area apart from the outer peripheral surface of the spraying head are controlled in the circumferential direction of the spraying head to thereby control the diffusion of paint particles radiated centrifugally from the spraying head. However, once the paint particles are diffused around the outer periphery of the spraying head by being radiated centrifugally from the spraying head, it is difficult to control the direction of diffusion of these paint particles by the above-described air stream in regard to the following points and such a control method is therefore inefficient and impractical:
(1) Since the paint particles themselves have a relatively large kinetic energy, it is necessary in order to change the direction of flight (diffusion) of the paint particles to form an air stream having a high velocity or a large width.
(2) An exceedingly large amount of air must be jetted out in order to cover the whole of the paint particles which have already been diffused around the outer periphery of the spraying head with an air stream which satisfies the conditions mentioned in (1).
(3) Since the diameter of the air outlet pitch circle is large, the size and weight of the coating apparatus are increased.
(4) Part of paint particles radiated from the spraying head adhere to portions of the apparatus which are in the vicinity of the air outlet ports, thus causing spit (a kind of paint defect). In order to prevent the occurrence of such an unfavorable phenomenon, the air output ports must be disposed more rearwardly of the spraying head, and it is necessary to jet out an increased amount of air in order to control the spray pattern.
For the purpose of obtaining an elliptical spray pattern, one sort of rotating spraying type coating apparatus has been proposed which is provided with a multiplicity of first air outlet ports disposed annularly and a second air outlet ports for jetting out an air stream which is used to distort the stream of air jetted out from the first air outlet ports (see Japanese Patent Laid-Open No. 57-180460 and Japanese Utility Model Laid-Open No. 59-127762). In these coating apparatus, however, a second stream of air is collided with an annularly air stream which is formed forwardly of the outer periphery of the spraying head so as to control the velocity and width of the latter air stream in the circumferential direction of the spraying head, thereby controlling the direction of the diffusion or paint particles radiated centrifugally from the spraying head, and the basic idea for design is deemed to be the same as that of the above-described coating apparatus (Japanese Utility Model Laid-Open No. 54-24270). Accordingly, these apparatuses have the same problems and therefore are impractical.